AAPM TG-142 (Linac QA)
AAPM Task Group 142 — the consensus quality-assurance framework for medical linear accelerators in the United States. Published in 2009 (with subsequent updates and adjacent task-group reports), TG-142 defines the daily, monthly, and annual checks every linac must pass for clinical use. Signed by a Qualified Medical Physicist (QMP). A linac that fails TG-142 is not clinical-use-ready, and patients are not treated until corrective action restores compliance.
Daily checks (technologist + physicist supervision)
- Beam output constancy — daily check against a baseline; tolerance ~3% on most parameters.
- Mechanical and safety interlocks — door, audio, video, beam-on indicators, emergency-off.
- Laser alignment — to isocenter.
- Imaging system — kV / kV CBCT, MV portal — basic functional check.
- Couch position indicators.
Monthly checks (physicist)
- Output constancy at all energies and modes (photon, electron, FFF).
- Beam profile constancy — flatness, symmetry, energy.
- MLC position accuracy — pictureframe, leaf-position tests, picket-fence.
- Imaging system — kV / MV / CBCT spatial accuracy, geometric calibration.
- Mechanical — gantry / collimator / couch angle accuracy, isocenter verification.
- Safety — radiation-survey checks, dose-rate verification.
Annual checks (physicist)
- Comprehensive beam-data verification — calibration against NIST-traceable reference.
- MLC end-to-end — leaf-position accuracy, leaf-speed, transmission, picket-fence at all gantry angles.
- Imaging chain — kV CBCT geometric accuracy, image quality, dose, MV imager calibration.
- Couch — 6 DoF accuracy on PerfectPitch / HexaPOD-equipped systems.
- Output linearity, energy stability, end-to-end SRS test for SRS programs.
- Radiation safety — vault shielding survey, area surveys, audit of personnel monitoring.
Adjacent task-group reports
TG-142 doesn't cover everything. Adjacent frameworks fill in:
- TG-100 — risk-based methodology for QA program design.
- TG-148 — TomoTherapy QA.
- TG-135 — robotic radiosurgery (CyberKnife).
- TG-198 — implementation guidance.
- MPPG 5.a / 8.b / 9.a — Medical Physics Practice Guidelines for IMRT, SRS, IGRT commissioning.
- TRS-483 — small-field dosimetry (IAEA / AAPM joint, SRS commissioning).
Why it matters to buyers
- Refurb purchases: a TG-142 baseline survey is a precondition for clinical use after install. Budget physicist labor in calendar weeks at commissioning.
- License-tier impact: FFF, RapidArc, HyperArc, SRS packages each add their own QA cadence and instrumentation requirements.
- Platform-specific QA workflows — TrueBeam has the most-mature QA tooling ecosystem; Versa HD, Halcyon, MR-Linac, and TomoTherapy each require platform-specific approaches.
- Failed-test downtime — a failed TG-142 check takes the unit out of clinical service until corrective action restores compliance; cancer schedules are time-sensitive.